1. Field of the Invention
The present invention relates to a semiconductor laser module.
2. Description of the Related Art
In a semiconductor laser module having an optical fiber coupling system in which light emitted from a packaged semiconductor laser is guided by a lens to an optical fiber, a core portion of the optical fiber along which the light propagates has a section size which is as small as several microns. When dust adheres to the core portion of an end face of the optical fiber, the transmission efficiency of light is largely lowered. A method of preventing dust from being produced in a light incident end face of an optical fiber has been proposed.
In a related art, even when an adhesive agent, a cleaning agent, a flux for soldering, or the like used in a process of assembling a semiconductor laser module remains in the module in a very small amount on the order of ppm, adherence or adsorption of such dust to an optical component possibly occurs. A method is known in which an optical fiber coupling system of a semiconductor laser module is hermetically isolated and sealed from the ambient air, and organics existing in the atmosphere inside the semiconductor laser module are caused to adhere to or to be adsorbed to an organic adsorbent such as activated charcoal (for example, see JP-A-2003-101116).
In the related art, since the optical fiber coupling system is isolated from the ambient air, however, there may arise the following problems (1) to (3).
(1) When the semiconductor laser module is used at a high or low altitude, a pressure difference is produced between the ambient air and the inside to deform the optical fiber coupling system, thereby causing variation of the transmission efficiency of light.
(2) When the semiconductor laser module is used at a high or low altitude, a pressure difference is produced between the ambient air and the inside to cause leakage in an incomplete hermetic sealing portion of the optical fiber coupling system, whereby a substance which may cause contamination is allowed to enter from the outside.
(3) When the humidity of the ambient air is high, moisture enters the inside through an incomplete hermetic sealing portion of the optical fiber coupling system. Even after the ambient humidity is lowered, the entering moisture stays inside, a change of the ambient temperature causes the moisture to condense to form dew, thereby adversely affecting the optical fiber coupling system.
There is another problem in that powder due to the adhesive agent scatters, and the optical system is contaminated, thereby lowering the transmission efficiency of light.